This invention relates generally to digital filter circuitry and more particularly, it relates to a digital receive filter circuit for use with a StarLAN (proposed specification IEEE P802.3-86/0.06G entitled "Physical Signaling, Medium Attachment, and Baseband Medium Specifications, Type 1BASE5") coded data transceiver.
In FIG. 1, there is shown a StarLAN (an acronym for Star Local Area Network) transceiver 10 which includes a receiver 12. The receiver 12 consists of a differential line receiver which is similar to the one that is commercially available from Advanced Micro Devices, Inc. of Sunnyvale, Calif. and designated by their part No. Am26LS32. The line receiver 12 has its inputs coupled to input terminals 2 and 4 for receiving differential input signals and converts the same to a single-ended digital data input signal R.times.D appearing at its output on terminal 14. Typically, the digital data input signal R.times.D is a Manchester encoded data transmission signal which is transmitted over a common communication cable defining a receive channel from another transceiver connected to the same cable. It has been encountered, in practice, that this input signal R.times.D, at the output terminal 14 is quite susceptible to line noise and transients which are passed through from the input terminals 2 and 4 of the line receiver 12.
In order to suppress false signals in the line receiver 12 due to interference from such line noise and transients, there has been attempted in the prior art of providing an analog filter 18 using discrete components which is interconnected between the output terminal of the line receiver 12 and a line 16 which is connected to other parts of the transceiver. While such a prior art analog filter is believed to perform adequately, it does not readily lend itself to miniaturization as required in hitech digital communication networks.
It would therefore be desirable to provide a digital receive filter circuit for generating appropriate filtering to avoid false triggering due to interference at the output of a line receiver. By selection of circuit components and functions, the digital receive filter circuit of the instant invention is capable of being fabricated with a StarLAN coded data transceiver as a part of a single monolithic integrated circuit in a compact and efficient configuration.